MOS semiconductor device isolated by a device isolation film

ABSTRACT

A MOS semiconductor device isolated by a trench device isolation region includes a p-channel MOS field effect transistor having a source/drain region with a length in the channel direction that is not more than 1 micrometer, and a gate length that is not more than 0.2 micrometers. The n-channel MOS field effect transistor is designed so that a face of the sourced/drain region in parallel to the gate width direction is adjacent to the device isolation film with the inserted silicon nitride film, and a face of the source/drain region parallel to the gate length direction is adjacent to the device isolation film including the silicon oxide film only.

The present Application is a Divisional Application of U.S. patentapplication Ser. No. 10/498,377, filed on Sep. 17, 2004, now U.S. Pat.No. 7,193,269.

TECHNICAL FIELD

The present invention relates to a MOS semiconductor device having a MOSfield effect transistor, and more particularly to a MOS semiconductordevice including at least one of a p-channel MOS field effect transistorand an n-channel MOS field effect transistor which are improved inON-current.

BACKGROUND ART

Improvements in performances of MOS transistors and CMOS have been madeby shrinkage or scaling down thereof, for example, shortening a channellength and a reduction in thickness of a gate insulating film. Areduction in thickness of the gate insulating film and a minimum size ordimension for process have become closer to the limitations. A furtherimprovement in performance can not depend upon the limited shrinkage orscaling down of the device, but should depend upon any other measuresthan the shrinkage or scaling down of the device.

One of the improvements in performance of the device is a technique ofapplying a stress to a channel region for improving a carrier mobility,so called strained-Si channel technique. The followings are thetechnique for forming a device in an strained Si wide region. A firstconventional method is that an Si epitaxial growth over a single crystalSiGe relaxed layer is made, so that an MOS is formed in the Si epitaxiallayer. A second conventional method is that an extremely thin SOI isheated at a high temperature and then cooled to room temperature, and inthis cooling process, a strain is generated in the SOI. This strain isutilized.

The first conventional method has problems for how to keep a surfaceplanarity of Si layer grown over the relaxed layer as well as how toreduce defects in the related layer or the strained Si layer. The firstconventional method is not practically realizable. In accordance withthe first conventional method, a strain of at most 0.3 GPa can beintroduced, thereby making it difficult to obtain a sufficiently highmobility.

Different from the technique for introducing the uniform strain into thewide area of the substrate, another technique is present for controllinga lattice strain of a channel or a mobility of carriers by utilizing astress caused by the device structure or process, particularly a deviceisolation technique. Japanese laid-open patent publication No.2001-28341 discloses that an Si layer is deposited by a sputteringmethod over an SiO₂ layer, which may be compressible and is depositedover an Si substrate. Then, the Si layer is made into an Si island forsubsequent heat treatment to cause a compression of the SiO₂ film and acrystallization of the Si film, whereby a compressive strain isintroduced into a p-channel MOS field effect transistor. Even the heattreatment is made to the Si film deposited over the amorphous SiO₂ film,then the Si film is not crystallized. The compressive strain asintroduced provides a mobility of polycrystalline. This is unsuitablefor the cases that the MOS transistor or the CMOS is formed over thesingle crystal Si.

Japanese laid-open patent publication No. 2000-36567 discloses that athickness of an oxide film buried in an SOI wafer and a condition forforming a field oxide film for forming an island of the Si film over theSOI wafer are properly set to allow the Si island to accept thecompressive stress. A gate delay time of the p-channel MOS field effecttransistor in accordance with this method is smaller than that of thep-channel MOS field effect transistor formed over a bulk Si substrate.An increase in a mobility of holes is confirmed. Since the strainintroduced into the island is the compressive strain, the increase inthe mobility is the opposite effect to the n-channel MOS field effecttransistor. For this reason, it is not anticipated to improve theperformance of CMOS.

Japanese laid-open patent publication No. 11-54756 discloses that eachmobility of electron and hole inbiaxial-compressive-and-tensile-strained Si are calculated toinvestigate what strain is effective to improve the performance of CMOS.As a result of the investigation, it was confirmed that the compressivestrain of 1%-2% improves electron and hole mobilities. An Si islandstructure was proposed for realizing the strained Si, wherein thestructure comprises an SOI isolated in LOCOS method. The strain of 1%-2%is to generate crystal defect and break Si crystal. Practicalrealization of this conventional method is difficult.

An issue of the present invention is to solve the above-describedproblems with the prior art.

An object of the present invention is to improve an ON-current of ap-channel MOS field effect transistor and an n-channel MOS field effecttransistor for controlling a strain of a channel region, wherein astress caused by a device structure is controlled by a method highlymatched to the conventional process as well as to provide a CMOScomprising an n-channel MOS field effect transistor and a p-channel MOSfield effect transistor which are improved in ON-current.

DISCLOSURE OF INVENTION

In order to achieve the above objects, the present invention provides anMOS semiconductor device having a p-channel MOS field effect transistorwith a channel which has a compressive strain in a channel direction anda compressive strain in a gate width direction, wherein the compressivestrain in the channel direction is larger than the compressive strain inthe gate width direction.

It is preferable that the p-channel MOS field effect transistor has agate electrode which has a gate length of not less than 0.2 micrometersand has a source/drain length of less than 1 micrometer.

In order to achieve the above objects, the present invention provides asemiconductor device including a p-channel MOS transistor isolated by adevice isolation film buried in a trench groove, and at least a part ofthe device isolation film, which is adjacent to parallel two sides, inparallel to a gate width direction, of source/drain regions of thep-channel MOS field effect transistor, comprises a silicon oxide film,and at least a part of the device isolation film, which is adjacent toparallel two sides, in parallel to a channel direction, of thesource/drain regions of the p-channel MOS field effect transistor,comprises a silicon nitride film.

It is preferable that an n-channel MOS field effect transistor is formedover a substrate, over which the p-channel MOS field effect transistoris formed.

In order to achieve the above objects, the present invention provides asemiconductor device including an n-channel MOS field effect transistorwith a channel region which has a tensile strain in a channel directionor a gate width direction and another compressive strain in the gatewidth direction or the channel direction, wherein the tensile strain inthe channel direction or the gate width direction is larger than theother tensile strain in the gate width direction or the channeldirection.

In order to achieve the above objects, the present invention provides aMOS semiconductor device having an n-channel MOS field effect transistorisolated by a device isolation film buried in a trench groove, and atleast a part of the device isolation film adjacent to at least paralleltwo sides of source/drain regions of the n-channel MOS field effecttransistor comprises a silicon nitride film.

BRIEF DESCRIPTIONS OF DRAWINGS

FIG. 1 is a schematic view of a p-channel MOS field effect transistorwith a long source/drain length for investigation on a relationshipbetween a lattice strain and an ON-current in a channel region thereofin a first embodiment of the present invention.

FIG. 2 is a schematic view of a p-channel MOS field effect transistorwith a short source/drain length for investigation on a relationshipbetween a lattice strain and an ON-current in a channel region thereofin a first embodiment of the present invention.

FIG. 3 is a view showing a measured position of a region, for which alattice strain was measured.

FIG. 4 is a view showing a distribution of a lattice strain in a channeldirection in samples of two source and drain lengths.

FIG. 5 is a graph showing a dependency of ON-current upon a source/drainlength in a p-channel MOS field effect transistor.

FIG. 6 is a schematic view showing a sectioned structure of an STI-typedevice isolation film with an inserted silicon nitride film in a secondembodiment of the present invention.

FIG. 7 is a view showing a distribution of a lattice strain in a channeldirection of an STI-type device isolation film with an inserted siliconnitride film and another STI-type device isolation film free of anysilicon nitride film in a second embodiment of the present invention.

FIG. 8 is a sectioned view of an n-channel MOS field effect transistorwith an inserted silicon nitride film in a second embodiment of thepresent invention.

FIG. 9 is a sectioned view of a CMOS improved in performance by animproved ON-current of a p-channel MOS field effect transistor in athird embodiment of the present invention.

FIG. 10 is a sectioned view of a CMOS improved in performance by bothimproved ON-currents of n-channel and p-channel MOS field effecttransistors in a fourth embodiment of the present invention.

FIG. 11 is a sectioned view of a CMOS improved in performance by bothimproved ON-currents of n-channel and p-channel MOS field effecttransistors in a fifth embodiment of the present invention.

FIG. 12 is a sectioned view of a CMOS improved in performance by bothimproved ON-currents of n-channel and p-channel MOS field effecttransistors in a sixth embodiment of the present invention.

FIG. 13 is a view showing a distribution of a strain in a channeldirection in the presence and absence of a silicon nitride film.

FIG. 14 is a schematic view of a p-channel MOS field effect transistorwith a short source/drain length for investigation on a relationshipbetween a lattice strain and an ON-current in a channel region thereofin a seventh embodiment of the present invention.

THE BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will be described in detailswith reference to the drawings.

First Embodiment

The present inventors investigated a channel region with a strainintroduced by an STI (shallow trench isolation)-type device isolationregion as well as an influence of this strain to an ON-current. For thispurpose, two p-channel MOS field effect transistors were prepared andmeasured in lattice strain of channel region and in ON-current, whereinthe two p-channel MOS field effect transistors are different in adistance L′ between the device isolation film and the channel orsource/drain length as shown in FIGS. 1 and 2. FIG. 1 shows a firstp-channel MOS field effect transistor with a long source/drain length.FIG. 2 shows a second p-channel MOS field effect transistor with a shortsource/drain length.

As shown in FIG. 1, the first p-channel MOS field effect transistor hasthe following structure. An active region is isolated by an STI (shallowtrench isolation)-type device isolation film 2 over a silicon substrate1. A gate insulation film (not illustrated) is formed over the activeregion. A gate electrode 3 is formed over the gate insulation film. Thegate electrode 3 has a gate length of 0.11 micrometers and comprises apolysilicon. Source/drain regions comprising diffusion layers 4 areformed by using the gate electrode 3 as a mask. Each of the source/drainregions has a source/drain length L′ of 8.0 micrometers. Side walls 5are formed on side walls of the gate electrode. A cobalt silicide film 6is formed on surfaces of the diffusion layers 4 forming the source/drainregions and the gate electrode 3, and the cobalt silicide film 6 isself-aligned to the side walls 5. An inter-layer insulator 7 coats asubstrate surface. Contact holes are formed in the inter-layer insulator7, wherein the contact holes are positioned over the diffusion layers 4and the gate electrode top. Contact plugs 8 burying the contact holesare formed, thereby forming the first p-channel MOS field effecttransistor.

As shown in FIG. 2, the second p-channel MOS field effect transistor hasthe following structure. An active region is isolated by an STI (shallowtrench isolation)-type device isolation film 2 over a silicon substrate1. A gate insulation film (not illustrated) is formed over the activeregion. A gate electrode 3 is formed over the gate insulation film. Thegate electrode 3 has a gate length of 0.11 micrometers and comprises apolysilicon. Source/drain regions comprising diffusion layers 4 areformed by using the gate electrode 3 as a mask. Each of the source/drainregions has a source/drain length L′ of 0.5 micrometers. Side walls 5are formed on side walls of the gate electrode. A cobalt silicide film 6is formed on surfaces of the diffusion layers 4 forming the source/drainregions and the gate electrode 3, and the cobalt silicide film 6 isself-aligned to the side walls 5. An inter-layer insulator 7 coats asubstrate surface. Contact holes are formed in the inter-layer insulator7, wherein the contact holes are positioned over the diffusion layers 4and the gate electrode top. Contact plugs 8 burying the contact holesare formed, thereby forming the second p-channel MOS field effecttransistor. The second p-channel MOS field effect transistor isdifferent in the source/drain length only from the first p-channel MOSfield effect transistor.

Measurements of lattice strain of the channel region and the ON-currentwere then made to the first p-channel MOS field effect transistor andthe second p-channel MOS field effect transistor.

The measurement of the lattice strain was made by using a convergentelectron diffraction method utilizing a transmission electronmicroscope. In this method, a convergent electron beam with a diameterof not more than 1 nanometer is irradiated on the sample in order toobtain a diffraction image. Taking into account a dispersion ofelectrons, it is possible to measure a strain at a specified site of thesample at a spatial resolution of about 10 nm. Details of the measuringmethod and the analyzing method of the diffraction image are describedin Japanese laid-open patent publication No. 2000-9664.

FIG. 3 is a view showing a measuring position of a region, to which alattice strain measurement was made. In each sample, lattice strainmeasurements were made at each numbered position. Respective distancesof the measured positions from Si surface or respective depths from thesubstrate surface are uniform at about 10 nm.

FIG. 4 shows a distribution of lattice strain in a channel direction ofeach of the first p-channel MOS field effect transistor of L′=8micrometers and the second p-channel MOS field effect transistor ofL′=0.5 micrometers. The channel direction is a direction along whichcarriers travel, and corresponds to a gate length direction. A directionperpendicular to the channel direction corresponds to the gate widthdirection. In FIG. 4, a horizontal axis corresponds to numbers ofmeasuring positions in FIG. 3, wherein a measuring point 5 correspondsto a channel region directly under the gate electrode. A vertical axisrepresents a lattice strain, wherein a positive direction of thevertical axis represents a tensile stress, while a negative direction ofthe vertical axis represents a compressive stress.

A comparison of a value at a measuring point 5 directly under the gateelectrode is made. The first p-channel MOS field effect transistor ofL′=8 micrometers has a lattice strain in a channel direction of −7×10⁻⁴at a measuring point 5 directly under the gate electrode. In contrast,the second p-channel MOS field effect transistor of L′=0.5 micrometershas a lattice strain in a channel direction of −2.6×10⁻³ at a measuringpoint 5 directly under the gate electrode. The first and secondp-channel MOS field effect transistors have compressive strains oflattice at the measuring point 5 directly under the gate electrode. Itis demonstrated that as the source/drain length L′ is decreased, thenthe absolute value of this compressive strain is increased, and alsothat as the source/drain length L′ is increased, then the absolute valueof this compressive strain is decreased. This cause is that thediffusion layer 4 forming the source/drain defined by the trench deviceisolation film receives the compressive strain which is increased bydecrease of the source/drain length L′. Adjustment to the source/drainlength L′ may adjust the lattice strain caused by the channel region.

FIG. 5 shows a dependency of ON-current upon the source/drain length L′of the p-channel MOS field effect transistor. If the source/drain lengthL′ is ranged from 1.0 micrometer to 10 micrometers, then almost novariation in ON-current is caused. If the source/drain length L′ is lessthan 1 micrometer, then an increase in the ON-current is caused upondecrease of the source/drain length L′. The ON-current at L′=0.3micrometers is higher by about 10% than the ON-current at L′=5.0micrometers. The above experimental result shows that the decrease ofthe source/drain length L′ increases the compressive strain of thelattice structure of the channel region. The increase in the compressivestrain causes the increase of the hole mobility to increase theON-current.

In accordance with the present embodiment, no measurement is made to astrain in a gate width direction or a vertical direction to a paper ofFIG. 3. Notwithstanding, the device isolation film is present in thisdirection in the actual device, for which reason a compressive strain isalso present unless any particular relaxation process is made. Thepresence of the gate electrode over the active region of the p-channelMOS field effect transistor does not generate any isotropic strain andalso does not generate any compressive strain in the gate widthdirection as large as the compressive strain in the channel direction.As the source/drain length L′ becomes shorter, then the compressivestrain of the lattice structure in the channel direction becomesdominant over the compressive strain of the lattice structure in thegate width direction. Shortening the source/drain length L′ to less than1 micrometer introduces the compressive strain in the channel directionwhich is larger than the compressive strain in the gate width direction.

The source/drain length of the second p-channel MOS field effecttransistor shown in FIG. 2 is shorter than 1 micrometer, for example,L′=0.5 micrometers. Namely, in the second p-channel MOS field effecttransistor, the compressive strain in the channel direction is largerthan and dominant over the compressive strain in the gate widthdirection.

The compressive strain of −2.6×10⁻³ in the channel direction at L′=0.5micrometers is as large as any crystal defect may theoretically begenerated. In accordance with this embodiment, such large strain isgenerated in an extremely limited area directly under the gateelectrode, wherein no crystal defect is generated in such the limitedarea. For example, the gate length of the first and second p-channel MOSfield effect transistors is 0.11 micrometers. The large strain ispresent only in such the local area, whereby no crystal defects aregenerated. In accordance with the present embodiment, the gate length is0.11 micrometers as one example. Notwithstanding, if the gate length isnot more than 0.2 micrometers, no crystal defect is generated.

It is, therefore, preferable that the gate length of the transistor ofthe present embodiment is not more than 0.2 micrometers.

The p-channel MOS field effect transistor in accordance with thisembodiment allows adjustments to the compressive strain in the gatewidth direction and the compressive strain in the channel direction ofthe lattice structure of the channel region by only adjustment to thesource/drain length in design process without changing to themanufacturing processes.

Second Embodiment

In accordance with the above-described first embodiment, the p-channelMOS field effect transistor is improved in ON-current by applying thecompressive strain in the channel direction to the p-channel MOS fieldeffect transistor. Application of the compressive strain in the channeldirection to the n-channel MOS field effect transistor causes decreaseof the ON-current. It is necessary for the n-channel MOS field effecttransistor to introduce a tensile strain in the channel direction intothe n-channel MOS field effect transistor to improve the ON-currentthereof.

In accordance with this second embodiment, a silicon nitride film isinserted into the STI-type device isolation film to introduce thetensile strain in the channel direction into the n-channel MOS fieldeffect transistor to improve the ON-current thereof. FIG. 6 showsschematically the section of the device isolation film with the insertedsilicon nitride film. The STI-type device isolation comprises a siliconoxide film 2 a adjacent to an internal wall of a trench groove, asilicon oxide film 2 c burying the trench groove, a silicon nitride film2 b interposed between the silicon oxide film 2 a and the silicon oxidefilm 2 c.

FIG. 7 shows a measured result of a distribution of the lattice strainin the diffusion layer (as represented by broken line) in one case thatthe STI-type device isolation structure is free of any inserted siliconnitride film as well as another measured result of another distributionof the lattice strain in the diffusion layer (as represented by realline) in other case that the STI-type device isolation structure withthe inserted silicon nitride film. A horizontal axis represents adistance from an edge of the trench of FIG. 6. If the silicon nitridefilm is not inserted, the compressive strain in the channel direction ispresent. In contrast, if the silicon nitride film is inserted, thetensile strain in the channel direction is present. This tensile strainis caused by a lateral strain to an intrinsic stress of the siliconnitride film.

The structure of the sample and the lattice strain are different betweenthe case that the silicon nitride film of FIG. 7 is not inserted and theother case of L′=0.5 micrometers in FIG. 4. Namely, in FIG. 4. Themeasurement is made to the sample of the device structure having the MOSfield effect transistor including the gate electrode. In FIG. 7, themeasurement is made to the sample of the device structure having onlythe device isolation region, for which reason the distribution of thelattice strain is different between both cases. The results shown inFIGS. 4 and 7 are not inconsistent to each other.

FIG. 8 is a cross sectioned view of the n-channel MOS field effecttransistor in accordance with the second embodiment of the presentinvention. In FIG. 8, the same reference numbers are allocated to thesame parts as in FIG. 1. Duplicate descriptions will be omitted. Inaccordance with this embodiment, the device isolation film has atriple-layered structure of a silicon oxide film 2 a, a silicon nitridefilm 2 b and a silicon oxide film 2 c. This structure generates atensile strain in the channel direction which is larger than anothertensile strain in the gate width direction, thereby to improve theON-current as compared to the n-channel MOS field effect transistorisolated by the device isolation film free of any inserted siliconnitride film.

The insertion of the silicon nitride film into the device isolation filmis achieved by that a part of the device isolation film comprises thesilicon nitride film. A variety of modification thereto may beavailable. It is, for example, possible that the entirety of the trenchgroove is buried with silicon nitride. Taking into account increasing aninterface state density with the silicon substrate, it is preferablethat the inner surface comprises the silicon oxide film. The quantity ofthe tensile strain depends upon the thickness of the silicon nitridefilm. It is preferable to select the structure of the device isolationfilm and the thickness of the silicon nitride film based on the quantityof the strain to be introduced.

In accordance with the present embodiment, the silicon nitride film isinserted into the device isolation film with the section parallel to apaper of the drawing. Notwithstanding, it is also possible to insert thesilicon nitride film into the device isolation film with the sectionvertical to a paper of the drawing.

The preferable gate length is as mentioned in the first embodiment.

The p-channel MOS field effect transistor in accordance with thisembodiment allows adjustments to the compressive strain in the gatewidth direction and the compressive strain in the channel direction ofthe lattice structure of the channel region by only adjustment to thesource/drain length in design process without changing to themanufacturing processes.

Third Embodiment

FIG. 9 is fragmentary plan and sectional views showing a CMOS structurein accordance with the third embodiment of the present invention. inFIG. 9, the same reference numbers are allocated to the same parts asshown in FIGS. 1 and 2. Duplicate descriptions will be omitted. In thethird embodiment shown in FIG. 9, a p-well 1 a and an n-well 1 b areformed over a silicon substrate 1. An n-channel MOS field effecttransistor and a p-channel MOS field effect transistor are formed overthose wells. As shown in the same drawing, in accordance with thisembodiment, the CMOS structure comprises the n-channel MOS field effecttransistor with a long source/drain length L′ and the p-channel MOSfield effect transistor with a short source/drain length L′. If thesource/drain length L′ is short, then the hole mobility is increased,while the electron mobility is decreased. If both the n-channel andp-channel MOS field effect transistors have short source/drain length,then the n-channel MOS field effect transistor is deteriorated inperformance, whereby any improvement in performance of the CMOS devicecan be expected. Therefore, the source/drain length of the n-channel MOSfield effect transistor is increased to avoid any drop of the electronmobility by the compressive strain. It is preferable that thesource/drain length is not less than 1 micrometer for avoiding anyinfluence of the compressive strain. On the other hand, the source/drainlength of the p-channel MOS field effect transistor is shorter than 1micrometer, and typically L′=0.5 micrometers as mentioned above in thefirst embodiment. In the p-channel MOS field effect transistor, thecompressive strain in the channel direction is larger than and dominantover the compressive strain in the gate width direction. The CMOS is sodesigned that the source/drain length of the n-channel MOS field effecttransistor is longer than the source/drain length of the p-channel MOSfield effect transistor.

The preferable gate length is as mentioned in the first embodiment.

Each of the p-channel and n-channel MOS field effect transistors inaccordance with this embodiment allows adjustments to the compressivestrain in the gate width direction and the compressive strain in thechannel direction of the lattice structure of the channel region by onlyadjustment to the source/drain length in design process without changingto the manufacturing processes.

Fourth Embodiment

FIG. 10 is fragmentary plan and sectional views showing a CMOS structurein accordance with the fourth embodiment of the present invention. InFIG. 10, the same reference numbers are allocated to the same parts asshown in FIGS. 8 and 9. Duplicate descriptions will be omitted. In thefourth embodiment, a CMOS structure comprises the n-channel MOS fieldeffect transistor and the p-channel MOS field effect transistor. Thep-channel MOS field effect transistor is isolated by the normal STIfilm, and the source/drain length is designed to be not more than 1micrometer. In the n-channel MOS field effect transistor, a face of thesource/drain region parallel to the gate width direction is adjacent tothe STI film with the inserted silicon nitride film. In the channelregion of the p-channel MOS field effect transistor, the compressivestrain in the channel direction is larger than the compressive directionin the gate width direction. In the channel region of the n-channel MOSfield effect transistor, the tensile strain in the channel direction islarger than the tensile direction in the gate width direction. In boththe p-channel and n-channel MOS field effect transistors, it is possibleto improve the ON-current and realize the high performance of CMOS. Forthe device isolation film of the n-channel MOS field effect transistor,it is possible that the silicon nitride films are inserted into all ofthe STI film adjacent to the source/drain regions of the n-channel MOSfield effect transistor.

The preferable gate length is as mentioned in the first embodiment.

The p-channel MOS field effect transistor in accordance with thisembodiment allows adjustments to the compressive strain in the gatewidth direction and the compressive strain in the channel direction ofthe lattice structure of the channel region by only adjustment to thesource/drain length in design process without changing to themanufacturing processes. The n-channel MOS field effect transistor inaccordance with this embodiment allows adjustments to the tensile strainin the gate width direction and the tensile strain in the channeldirection of the lattice structure of the channel region by onlyadjustment to the source/drain length in design process without changingto the manufacturing processes.

Fifth Embodiment

In accordance with the above-described four embodiments, the strain inthe channel direction is taken into account and is adjusted to improvethe device performance. It has been known that another strain in adirection perpendicular to the channel direction or in the gate widthdirection changes the hole mobility. A. Hamada et al., “A New Aspect OfMechanical Stress Effect SiN Scaled MOS Devices” IEEE Transactions onElectron Devices, 38 (1991) 895 discloses that application of thetensile stress of uniaxial stress in the perpendicular direction to thechannel direction increases both electron mobility and hole mobility,while application of the compressive stress of uniaxial stress in theperpendicular direction to the channel direction decreases both electronmobility and hole mobility.

FIG. 11 are fragmentary plan and sectional views showing CMOS structurein accordance with the fifth embodiment of the present invention. InFIG. 11, the same reference numbers are allocated to the same parts asshown in FIGS. 8 and 9. Duplicate descriptions will be omitted. In thefifth embodiment, a CMOS structure comprises the n-channel MOS fieldeffect transistor and the p-channel MOS field effect transistor. In thep-channel MOS field effect transistor, a face of the source/drain regionparallel to the channel direction is adjacent to the STI film with theinserted silicon nitride film. In the n-channel MOS field effecttransistor, a face of the source/drain region parallel to the channeldirection is also adjacent to the STI film with the inserted siliconnitride film. In accordance with this structure, the channel regions ofboth the p-channel and n-channel MOS field effect transistors receiveapplication of the tensile strain in the gate width directionperpendicular to the channel region, thereby improving electron mobilityand hole mobility.

The preferable gate length is as mentioned in the first embodiment.

Each of the p-channel and n-channel MOS field effect transistors is sodesigned that a face of the source/drain region parallel to the channeldirection is adjacent to the STI film with the inserted silicon nitridefilm, whereby applying the channel region with a tensile strain in thegate width direction perpendicular to the channel direction forimproving the electorn mobility and the hole mobility.

Sixth Embodiment

FIG. 12 are fragmentary plan and sectional views showing CMOS structurein accordance with the sixth embodiment of the present invention. InFIG. 12, the same reference numbers are allocated to the same parts asshown in FIG. 11. Duplicate descriptions will be omitted. In the sixthembodiment, the source/drain length of the p-channel MOS field effecttransistor is not more than 1 micrometer, and the n-channel MOS fieldeffect transistor is isolated by the STI film with the inserted siliconnitride film which encompasses the n-channel MOS field effecttransistor. This structure applies the compressive strain in the channeldirection and the tensile strain in the gate width direction to thep-channel MOS field effect transistor to the p-channel MOS field effecttransistor as well as applies the tensile strains in both the channeldirection and the gate width direction to the n-channel MOS field effecttransistor. This structure causes further improvements in the electronmobility and the hole mobility and also in the performance of the CMOSas compared to the fifth embodiment.

The preferable gate length is as mentioned in the first embodiment.

Seventh Embodiment

Utilization of a film stress at the top of the channel region is alsoavailable for applying a strain to the channel region. FIG. 13 shows adistribution of a strain in the channel direction in the presence andabsence of the silicon nitride film. FIG. 14 is a schematic view showinga p-channel MOS field effect transistor with a short source/drain lengthprepared for investigation on a relationship between the lattice strainin the channel region and the ON-current. In FIG. 14, the same referencenumbers are allocated to the same parts as shown in FIGS. 1 and 2.Duplicate descriptions will be omitted. In the seventh embodiment, aninterlayer insulator comprises a silicon nitride film 7 a as an etchingstopper and a silicon oxide film 7 b. In FIG. 13, the strains in thechannel direction are shown in the presence and absence of the siliconnitride film 7 b. Measuring positions correspond to numbers shown inFIG. 3. As can be seen from FIG. 13, the silicon nitride film coveringthe active region introduces the lattice strain in the channel directioninto the channel region locally, whereby the hole mobility is improved,ad the high speed performance of the p-channel MOS field effecttransistor is realized.

It is possible that the silicon nitride film 7 b is so formed ascovering the entirety of the substrate even the effect of improving theelectron mobility can not be expected. For this reason, it is alsopossible to selectively remove the silicon nitride film from theposition over the n-channel MOS field effect transistor. It is alsopossible to selectively form the silicon nitride film over the p-channelMOS field effect transistor. As coating materials, not only the siliconnitride film but also other materials causing a tensile strain in the Sisubstrate are also available. It should be noted that utilization of thefilm strain over the channel region causes application of one of thecompressive and tensile strains. The present embodiment may also beapplied in combination with the other embodiments.

INDUSTRIAL APPLICABILITY

As described above, in accordance with the MOS semiconductor device ofthe present invention, the source/drain length is adjusted or thenitride film is inserted in the isolation film in order to adjust thestrain in the channel region. In accordance with the present invention,control to the strain in the channel region is made to increase theON-currents of the p-channel and n-channel MOS field effect transistors.The p-channel and n-channel MOS field effect transistors areindependently controllable in strain, thereby avoiding that increase ofone ON-current causes decrease of another ON-current. In accordance withthe present invention, however, it is possible to increase theON-currents of the p-channel and n-channel MOS field effect transistorsfor realizing the high performance of the CMOS device without increasinga cost.

1. A semiconductor device including a p-channel MOS field effecttransistor with a channel region which has a compressive strain in achannel direction and a compressive strain in a gate width direction,wherein the compressive strain in the channel direction is larger thanthe compressive strain in the gate width direction, and wherein thechannel region of the p-channel MOS field effect transistor has atensile stress in the gate width direction.
 2. The semiconductor deviceas claimed in claim 1, wherein the p-channel MOS field effect transistorhas an active region having a compressive strain in the channeldirection, and wherein the compressive strain in the channel directionis locally increased in the channel region.
 3. The semiconductor deviceas claimed in claim 1, wherein the p-channel MOS field effect transistorhas a gate electrode with a gate length of not more than 0.2micrometers.
 4. The semiconductor device as claimed in claim 1, whereinthe channel region of the p-channel MOS field effect transistor has atensile stress in the gate width direction.
 5. The semiconductor deviceas claimed in claim 1, further including a stress applying film over asemiconductor substrate, and the stress applying film applying a stressto the channel region.
 6. The semiconductor device as claimed in claim1, wherein the stress applying film comprises a silicon nitride film. 7.A semiconductor device including an n-channel MOS field effecttransistor with a channel region which has a tensile strain in a channeldirection or a gate width direction and another compressive strain inthe gate width direction or the channel direction, wherein the tensilestrain in the channel direction or the gate width direction is largerthan the other tensile strain in the gate width direction or the channeldirection.
 8. The semiconductor device as claimed in claim 7, furthercomprising a p-channel MOS field effect transistor formed over asubstrate, over which the n-channel MOS field effect transistor isformed.
 9. The semiconductor device as claimed in claim 7, furtherincluding a stress applying film over a semiconductor substrate, and thestress applying film applying a stress to the channel region.
 10. Thesemiconductor device as claimed in claim 9, wherein the stress applyingfilm comprises a silicon nitride film.